1. Field of the Invention
The present invention relates to an image input apparatus, and more particularly, to an image input apparatus for images of persons and documents.
2. Description of the Related Art
Recently, with progress in computers and communication technology, the technological base for handling images with computers has expanded, and video cameras have become available as an image input means. For example, according to picture phone and videoconference systems, an image of a speaker or a document (such as a material of the conference) is input and transmitted over a distance to the other party. Since the provision of a separate video camera for the person and for the document represents a substantial cost, a combined use of one video camera for both the person and the document is usually considered.
FIG. 1 is an external view of a conventional video camera for images of persons and documents. Referring to FIG. 1, a camera head 110 is supported by a column 112 in such a manner that it can be directed horizontally or vertically downward. Since the camera head is changed between the cases when a person is picked-up and when a document is picked-up, the camera head 110 is provided with a function for changing the vertically downward direction in a picked-up image when, for example, the camera head 110 is directed downward. Outputs of the camera head 110 are supplied to a computer 114, displayed on a monitor screen, and then transmitted to remote areas.
Such image input apparatus and also a common video camera are provided with a correction circuit for automatically correcting a color balance, specifically, a white balance of pick-up images. In order to avoid the adverse influence of objects of different colors, technology is known in which the white balance is corrected by using only a signal from a white object (or of a color approaching white), or a signal having the potential of becoming such a signal (hereinafter, referred to as a white reference signal). For example, this technology is one in which only the white reference signal is extracted from a luminance signal and two types of color difference signals R-Y and B-Y to correct a gain of each color component of the pick-up image in such a manner that the extracted color difference component is allowed to approach zero.
In addition, technology is known in which, when a person is picked-up, the color balance is controlled in accordance with the color temperature of a light source (such as a sunlight, a fluorescent lamp or an incandescent lamp) in such a manner that the extracted color difference signal component is allowed to approach slightly to a warm color (R-Y&gt;0, B-Y&lt;0), thereby faithfully reproducing a realistic image without fading a color of the person's skin.
However, when a video camera provided with the white balance correction circuit adjusted for picking-up the person is used for picking-up the document, the color of the document is reproduced in somewhat reddish hues. Conversely, according to the white balance adjusted for color reproduction of the document, the color of the person's skin is reproduced with a slight fading when the person is picked-up.